freeCodeCamp/guide/english/certifications/javascript-algorithms-and-data-structures/intermediate-algorithm-scripting/sum-all-numbers-in-a-range/index.md

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Sum All Numbers in a Range

Sum All Numbers in a Range

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Problem Explanation

You need to create a program that will take an array of two numbers who are not necessarily in order, and then add not just those numbers but any numbers in between. For example, [3,1] will be the same as 1+2+3 and not just 3+1

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Hints

Hint 1

Use Math.max() to find the maximum value of two numbers.

Hint 2

Use Math.min() to find the minimum value of two numbers.

Hint 3

Remember to that you must add all the numbers in between so this would require a way to get those numbers.

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Solutions

Solution 1 (Click to Show/Hide)

function sumAll(arr) {
  var max = Math.max(arr[0], arr[1]);
  var min = Math.min(arr[0], arr[1]);
  var temp = 0;
  for (var i = min; i <= max; i++) {
    temp += i;
  }
  return temp;
}

sumAll([1, 4]);

Code Explanation

• First create a variable to store the max number between two.
• The same as before for the Smallest number.
• We create a temporary variable to add the numbers.

Since the numbers might not be always in order, using max() and min() will help organize.

Relevant Links

• Math.max()
• Math.min()
• For Loops

Solution 2 (Click to Show/Hide)

const sumAll = arr => {
  // Buckle up everything to one!
  const startNum = arr[0];
  const endNum = arr[1];

  // Get the count of numbers between the two numbers by subtracting them and add 1 to the absolute value.
  // ex. There are |1-4| + 1 = 4, (1, 2, 3, 4), 4 numbers between 1 and 4.
  const numCount = Math.abs(startNum - endNum) + 1;

  // Using Arithmetic Progression summing formula
  const sum = ((startNum + endNum) * numCount) / 2;
  return sum;
};

Code Explanation

• The formula for calculating the sum of a continuous range is "(startNum + endNum) * numCount / 2".
• arr[0] and arr[1] can either be startNum or endNum, order doesn't matter.
• We can get the count of numbers in range by "Math.abs(arr[0] - arr[1]) + 1".
• Applying the formula by plugging in the numbers.

Relevant Links

• Array.sort()
• Arithmetic Progression summing formula
• ES6 arrow function

Solution 3 (Click to Show/Hide)

function sumAll(arr) {
  var sum = 0;
  for (var i = Math.min(...arr); i <= Math.max(...arr); i++) {
    sum += i;
  }
  return sum;
}

sumAll([1, 4]);

Code Explanation

• Creating a variable sum to store the sum of the elements.
• Starting iteration of the loop from min element of given array and stopping when it reaches the max element.
• Using a spread operator (...arr) allows passing the actual array to the function instead of one-by-one elements.

Relevant Links

• Spread Operator
• Using Spread Operator in Math.max()